The enteric nervous system (ENS) consists of an elaborate network of neurons and glial cells that extends the entire length of the gastrointestinal tract and is essential for normal digestive function. In the central and peripheral nervous systems, glia are essential for the normal development, function and maintenance of neurons as well as the elaboration of structures such as myelin and the blood-brain barrier. In the ENS, the role of glial cells remains largely unknown. A classic approach to identifying the role of a cell population is to eliminate it and analyze the resulting effects on organ function. Previous studies taking this approach to ablate enteric glia in mouse models have reported that enteric glia are required for maintenance of the intestinal epithelial barrier and regulation of epithelial cell proliferation [4,5]. However, most of these mice developed significant intestinal inflammation, which is known to affect barrier function and epithelial turnover [6,7]. We have developed a mouse genetic model in which glial cells are selectively ablated by the inducible expression of a cellular toxin, resulting in loss of over 70% of enteric glia throughout the intestine within 7 day without any associated inflammation. This robust in vivo model of enteric glial loss now allows us to more precisely identify the role of enteric glia in key epithelial functions and to define th signaling pathways important for enteric glial function. In Aim 1, we will use this model to define critical interactions between glia, epithelial cells and neurons in the normal, non-inflamed intestine. As the physiologic role(s) of enteric glia are defined, we can begin to identify the signaling pathways involved. A prime candidate is the Neuregulin - ErbB signaling pathway known to mediate important interactions between neurons and glia in the central and peripheral nervous systems. Neuregulins (NRGs) are a family of trophic factors, typically expressed by neurons, which bind and activate the ErbB family of receptor tyrosine kinases expressed by glia. In Aim 2, we will use mouse models in which ErbB signaling in enteric glia is altered, and assess the effects on the ENS and on key epithelial functions. Taken together, findings from the proposed studies will significantly advance our understanding of ENS biology and yield new insights on how enteric glial defects contribute to digestive disease.